Taking low-dose aspirin at least three
times per week may reduce women's risk of breast cancer by up to 20 percent, a
new study suggests.

[Aspirin]

Researchers have found a link between
low-dose aspirin and reduced risk of breast cancer.

Study co-author Leslie Bernstein, Ph.D.,
of the Division of Biomarkers of Early Detection and Prevention at the City of
Hope Beckman Research Institute in Monrovia, CA, and colleagues recently
reported their findings in the journal Breast Cancer Research.

After skin cancer, breast cancer is the
most common cancer among women in the United States. This year, more than
252,000 new cases of invasive breast cancer will be diagnosed.

Previous research has suggested that
there may be a link between daily aspirin use and lower risk of breast cancer.

However, according to Bernstein and
colleagues, few studies have investigated the effects of aspirin use on the risk
of certain breast cancer subtypes, and it has been unclear as to whether
low-dose aspirin, or "baby" aspirin, protects against breast cancer.

With this in mind, the researchers set
out to determine the effects of low-dose aspirin - defined as a dose of 81
milligrams - on the risk of breast cancer overall, as well as its effects on
breast cancer subtypes defined by hormone receptor (HR) status and human
epidermal growth factor receptor 2 (HER2) expression.

HR status is whether or not the breast
cancer cells contain receptors for the hormones estrogen or progesterone. For
example, breast cancer cells that possess receptors for estrogen would be deemed
estrogen receptor-positive (ER-positive).

HER2 status is whether or not breast
cancer cells contains too many HER2 receptors, which can fuel breast cancer
growth.

HR-positive/HER2-negative breast cancer
risk cut by 20 percent

The researchers came to their findings
by analyzing the data of 57,164 women who were part of the California's Teachers
Study, which has monitored the health of more than 133,000 teachers and
administrators in California since 1995.

In 2005, the participants completed
questionnaires detailing their use of aspirin and other non-steroidal
anti-inflammatory drugs (NSAIDs).

By January 2013, 1,457 women had
developed invasive breast cancer. Of these cases, 998 were
HR-positive/HER2-negative, 138 were HR-negative/HER2-negative, 120 were
HR-positive/HER2-positive, and 44 were HR-negative/HER2-positive. Data on HR and
HER2 status were missing for the remaining 157 women.

Overall, the researchers found that
women who reported using low-dose aspirin at least three times weekly were 16
percent less likely to develop breast cancer, compared with women who used
low-dose aspirin less frequently.

Looking at breast cancer subtypes, the
team found that the risk of developing HR-positive/HER2-negative breast cancer
was 20 percent lower for women who took low-dose aspirin at least three times
per week.

No link was found between the use of
other NSAIDs and the risk of breast cancer, the team reports.

"We also did not find associations with
regular aspirin since this type of medication is taken sporadically for
headaches or other pain, and not daily for prevention of cardiovascular
disease," notes lead author Christina A. Clarke, Ph.D., from the Cancer
Prevention Institute of California.

Their findings remained after accounting
for a number of possible confounding factors, including the use of hormone
therapy and a family history of breast cancer.

'Our data are intriguing'

The study was not designed to pinpoint
the mechanisms by which low-dose aspirin may lower the risk of breast cancer,
but the researchers speculate that it may be down to the drug's
anti-inflammatory effects.

Additionally, the team notes that
aromatase inhibitors are used to treat ER-positive breast cancers. Since aspirin
is a weak aromatase inhibitor, this may partly explain its protective effect
against HR-positive breast cancers.

Overall, the researchers believe that
their findings suggest that low-dose aspirin could be effective for the
prevention of breast cancer, but they stress that further studies are needed
before recommendations can be made.

The authors conclude:

"Our data are intriguing as regards the
role of low-dose aspirin in breast cancer prevention but this question should be
revisited in cohorts with larger numbers of incident breast cancers, in which HR
and HER2 status are also recorded."